In the past, various methods of applying a magnetic recording substance to a moving web (hereinafter often referred to simply as a "web") have been employed including roller application, gravure application, extrusion application and slide bead application, combinations of these with doctor systems, and so forth.
Recently, a method of extrusion application and a method of applying a magnetic recording substance to a web while pushing an extrusion application head to the web without supporting the web on the reverse side thereof have been used in order to increase the speed of the application of the substance in the form of a film of small thickness and prevent defects such as the formation of a coagulated projection. In the latter method, the web and the extruder application head are in contact with each other when a liquid containing the magnetic recording substance is not being poured out. However, in that method, when the application of liquid to the web is started, a pool of liquid or liquid accumulation forms in the narrow gap between the web and the extrusion application head, so that the application of liquid to the web is performed without bringing the web into contact with the extrusion application head.
The above-mentioned methods are well-known because they are those disclosed in Japanese Patent Laid-Open Gazettes Nos. 57-84771, (U.S. Pat. No. 4,480,583) 58-104666, 59-94657, 58-189070 and 58-202075, and so forth.
In the above-mentioned well-known art, it was not clear what state or condition of the liquid accumulation between the application head and the web had which enabled the application of the liquid to the web, what conditions made the surface of the applied liquid good, and so forth. However, it has been very important to find out what conditions enable the proper application of the liquid in various quanities such as 5 cc./m.sup.2 to 100 cc./m.sup.2 at different application speeds to webs of various thicknesses.